SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<script src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.js"></script>
<form id="myForm">
    <select name="category">
        <option>---</option>
        <option>Category 1</option>
        <option>Category 2</option>
        <option>Category 3</option>
    </select>
    <input type="text" name="text" />
    <input type="submit" value="Test" />
</form>

JavaScript

jQuery.validator.addMethod("notEqual", function(value, element, param) {
  return this.optional(element) || value != param;
}, "Please choose a value!");

$('#myForm').validate({
    rules: {
        text: {
              required: true
        },
        category: {
            required: true,
            notEqual: "---"
        }
    },
    messages: {
        text: {
            required: "Text required"
        },
        category: {
            required: "Category required"
        }
    }
});